1. Technical Field
This invention relates generally to distribution of data signals in a home environment, and more particularly to a system and method for data distribution in the VHF/UHF band.
2. Description of Related Art
WiFi (Wireless Fidelity) is the trade name for the global set of 802.11 standards drafted for wireless Local Area Networks (LAN); any standard Wi-Fi device will work anywhere in the world. WiFi is one of the most popular wireless technologies; it is widely available in public hotspots, homes, and campuses worldwide, being supported by nearly every modern personal computer, laptop, most advanced game consoles, printers, and many other consumer devices. Routers which incorporate a Digital Subscriber Line (DSL) modem or a cable modem and a Wi-Fi access point, often set up in homes and other premises, provide Internet access and internetworking to all devices connected (wirelessly or by cable) to them.
Wi-Fi uses both single carrier direct-sequence spread spectrum radio technology (812.11b) and multi-carrier Orthogonal Frequency Division multiplexing (OFDM) radio technology (e.g. 802.11a, g, j, n). The Institute for Electronic and Electrical Engineers (IEEE) has established a set of standards for Wireless Local Area Network (WLAN) computer communication, collectively known as the IEEE 802.11 standard that are applicable to Wi-Fi signals.
The 802.11a standard uses OFDM radio technology in the 5 GHz U-NII band, which offers 8 non-overlapping channels and provides data rates of up to 54 Mbps. Another standard that uses OFDM is 802.11g, which attempts to combine the best features of the 802.11a and 802.11b standards. It uses enables data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, and the 2.4 GHz frequency for greater range. The 802.11j standard is an amendment designed especially for Japanese markets. It allows WLAN operation in the 4.9 to 5 GHz band to conform to Japanese rules for radio operation for indoor, outdoor and mobile applications. Finally, the 802.11n standard is a proposed amendment which improves upon the previous 802.11 standards by adding multiple-input multiple-output (MIMO) and many other newer features. Though there are already many products on the market based on the latest draft of this proposal, the 802.11n standard will not be finalized until December 2009.
In the U.S., 802.11a and 802.11g devices may be operated without a license. The 802.11a standard uses 20 MHz channels and operates in three unlicensed bands, known as the Unlicensed National Information Infrastructure (U-NII) bands; four 20 MHz channels are specified in each of these bands. The lower U-NII band, extending from 5.15 to 5.25 GHz, accommodates four channels with a 40 mW power limit; the middle U-NII band, extending from 5.25 to 5.35 GHz accommodates four channels with a 200 mW power limit; and the upper U-NII band, extending from 5.725 to 5.825 GHz, accommodates four 20 MHz channels with an 800 mW power limit.
An 802.11a signal uses OFDM modulation with 52 subcarriers, which include 48 data subcarriers and four pilot subcarriers; the subcarriers can be modulated using BPSK, QPSK, 16QAM or 64QAM. The total symbol duration is 4 μs, and includes a useful symbol duration of 3.2 μs and a guard interval of 0.8 μs, with a peak data rate of 54 Mbps. Subcarriers are spaced apart by 312.5 KHz so that the signal actually occupies a bandwidth of 16.25 MHz in theory.
In the United States, there are roughly 210 television (TV) broadcast regions and 1700 TV broadcasting stations. Currently, each TV station is assigned around eight radio frequency (RF) channels for NTSC broadcast, each channel occupying 6 MHz in the VHF/UHF spectrum. The Federal Communications Commission (FCC) has mandated that all full-power television broadcasts will use the Advanced Television Systems Committee (ATSC) standards for digital TV by no later than Feb. 17, 2009. All NTSC television transmissions will be terminated by that date. Following the NTSC TV switch-off, the FCC will allocate channels 2 through 51 to digital TV; channels 52 through 69 that occupy the lower half of the 700 MHz band have been already reallocated through auction to various advanced commercial wireless services for consumers.
The ATSC standard mandates a bandwidth of 6 MHz for each TV channel, use of Trellis Eight-Vestigial Side Band (8-VSB) modulation, and Reed-Solomon encoding. The TV receiver has some basic requirements to property decode the ATSC signal and provide good quality TV pictures. These requirements include that the TV Signal to Noise Ratio (SNR) is no less than 15.2 dB, a thermal noise floor of −106.2 dBm (dBm is the abbreviation for the power ratio measurement units), and a sensitivity of between −81 and −84 dBm etc.
As each TV station operating in a certain geographic region/area uses only a limited number of channels from the TV band, some digital channels remain unused in the respective area: this locally available spectrum is called “whitespace”.
It is expected that the FCC will allow the whitespace bands to be used only by devices that do not interfere with existing TV broadcast, wireless microphones, or Global Positioning System (GPS) systems deployed in that area. Consequently, the signals radiated by any whitespace devices/equipment operating in the ATSC spectrum must follow the FCC regulations so that the quality of the primary TV service will not be degraded by the signals using the nearby whitespace. Thus, the new whitespace devices should be designed so as to not affect the TV tuner sensitivity (−81˜−84 dB) and the TV receiver performance at SNR=15.2 dB.
A known solution for distributing multimedia content within a home is wireless high definition TV (HDTV). However, wireless HDTV requires a very high data rate (greater than 1 Gbps) and the 60 GHz band is not suitable for transmission over distances greater than 10 m. In addition, the quality of such a wireless link is not satisfactory and the cost is high.
Another known solution for distributing data and video within a home is WiFi. However, the WiFi band has uncontrollable interferences and the quality cannot be guaranteed.
Thus, there is a need to provide an inexpensive and efficient way to broadcast multimedia content within a confined environment, using wireless solutions. There is also a need to recycle the spectrum that is not used in a certain geographical area.